The use of explosives has been a main component in the overall arsenal of terrorists. Particularly based on various terrorist events, such as the Madrid rail bombing, the London Underground attack and the more recent exposure of possible attacks on U.S. bound flights from overseas, there is a prevailing need for a unified approach to the detection of liquid explosives, particularly in the aviation industry, but also in other mass transit modes of transportation. More specifically, there exists a need for technology to detect and distinguish hazardous liquids such as, homemade explosives, acids, oxidizers, and flammable liquids from benign liquids, such as medical liquids, baby formula, beverages, lotions, hygiene products, contact lens solutions and the like.
Currently there exists a bottle screening unit that is commercially available. This device is a diagnostic instrument that employs radio frequency technology (RF) to analyze liquids in containers. The device can discriminate between certain threat and benign liquids in only a couple seconds. The device is lightweight and portable, being about the size of a laptop computer. The device is designed to be installed in high traffic locations, such as airports, stadiums, courthouses, subway stations and the like. The device relies exclusively on RF or microwave technology and techniques thought to be originally developed for use in ground-penetrating radar systems. Basically, the device assesses dielectric constants for liquids in opened and unopened glass and plastic containers.
FIG. 1 depicts a process and device schematic used to discriminate between threat and benign liquids. In general, this known sensing device 10 functions by having a transmitting antenna 15 emit a radio frequency pulse or sending signal 20 which is scattered by liquid 25 in a glass or plastic container 30. The scattered sending signal reflects back from liquid 25 as a receiving signal 35 and is picked up by signal receiving antenna 40. A signal generating block 45 activates transmitting antenna 15 while signal receiving antenna 40 sends receiving signal 35 for processing by a period adjusting block 50 and a processing unit 55 for performing a predetermined computation on averaged waveforms in predetermined time-based ranges, and calculating an effective dielectric constant for liquid 25 in container 30. A so-called impulse method includes using a repetitive electromagnetic wave with a rapidly changing waveform section and short duration time. The process starts at signal generating block 45 and then proceeds to signal transmitting antenna 15; signal receiving antenna 40; period adjusting block 40; processing unit 55 and finally to an output block (not shown).
Examples of received waveforms for gasoline 60 and water 70 are shown in FIGS. 2A and 2B. The differences in the two waveforms are clearly obvious to the human eye. The decision to indicate a safe liquid or a threat liquid is made by comparing a threshold value on the received RF signal. For liquids with high dielectric constants, the received signal will exceed the threshold, while the received signal for liquids with low dielectric constant will not exceed the threshold. A table of known dielectric constants is illustrated in FIG. 3. The ovals in FIG. 3 emphasize the substantial difference in dielectric constant values between the benign 80 and threat liquids 90.
As indicated above, this known sensing device 10 is designed to detect certain threat liquids in plastic and glass bottles. Glass bottles may range from clear to various colors and plastic bottles, depending on their processing and thermal history, may be either amorphous (transparent) or semi-crystalline (opaque and white). Plastic bottles can also exhibit a multiplicity of colors. Unfortunately, with known sensing device 10, container 30 must have a bottom thickness of no greater than 0.5 mm for plastic bottles and less than 1 cm for glass bottles, while the bottom of container 30 for either plastic or glass bottles must be greater than 5 cm in diameter. In addition, device 10, as designed, is currently limited to detecting low dielectric explosives and flammable liquids including gasoline, light oil, paint thinner, ethanol, isopropyl alcohol, toluene, cyclohexane, kerosene, benzene, lighter fuel, and similar compounds.
Sensing devices using only RF sensors cannot detect hazardous material in metal containers. Therefore, some known arrangements teach using ultrasonic testing to detect hazardous liquids. However, prior versions of ultrasonic sensing devices cannot easily determine proper placement of a container on a sensing tray in the sensing device or can only detect large containers meeting specific characteristics. Likewise, removal of the container is also not automatically detected. Some known versions of the sensing device rely on the operator to properly place the container and then initiate testing with the sensor, which can result in testing errors if the operator is not careful.
Furthermore, to make an accurate measurement, ultrasonic sensing devices must know the material used to make the container holding the sample. Ultrasonic sensing devices typically relied on an operator to input whether the container is made of plastic, glass, metal or cardboard. In most cases, the type of material forming the container is readily apparent; however, in some cases appearances may be misleading. Many tubes, such as those holding toothpaste appear to be made of plastic but are actually formed from painted foil. Also, certain juice containers have a foil liner that cannot be readily observed by the operator. Such containers may thus be misidentified by the operator which can compromise the accuracy of the scan results. There is a desire in the art to eliminate this source of error and identify the material in each container automatically.
Also, the accuracy of known devices requires improvement to avoid misclassification of an unknown liquid as harmless or hazardous. The current RF systems compare a measured dielectric constant of an unknown sample to those dielectric constant values, stored in a database, that correspond to known materials. However, only using dielectric constants is not considered accurate enough and is only effective at determining low dielectric liquids from high dielectric materials. Such devices cannot tell the difference between two low dielectric liquids or two high dielectric liquids. There exists a need in the art to identify unknown liquids with more accuracy.
The present application is directed to adding to the accuracy of known systems. Particularly desirable upgrade parameters include an ability to determine a presence of a container having been placed in a container screening system along with an ability to determine a type of materials forming a container. The present application is also directed to more accurately detecting hazardous materials stored in a wider range of container materials and from an expanded number of benign and hazardous liquids.